20% time originated in 3M in 1950. They created sticky notes in that time, and is still widely used around the world. Earlier this year they tried the system again. Atlassian invested a year and $1 Million dollars to see how effective and productive it can be. If everything works out then it will be used every Friday and new inventions will be coming out of 3M in the next year or two.
Here is a link to their official blog:
http://blogs.atlassian.com/developer/